Heretofore, for window glasses for automobiles, ones having various curved shapes accommodated to designs of automobiles, are employed. These window glasses are produced by cutting a plate-shaped glass plate produced by e.g. a float method into a desired shape, heating and softening it and bending it by e.g. a press-forming. For a side window or a rear window, a tempered glass is commonly used, and by immediately air-cooling a heated glass plate after bending, a so-called tempered glass is produced.
Meanwhile, a laminated glass to be employed for windshields is a layered product constituted by two glass plates cut out to have substantially the same shape and a resin interlayer sandwiched therebetween. In general, a laminated glass is produced by placing two glass plates on a ring-shaped jig so that they are overlaid, and heating them in a furnace to bent them into a desired curved shape by their own weight. After the bending, they are gradually cooled without being air-cooled for tempering, as differently from the case of tempered glass. Thereafter, an interlayer (such as polyvinyl butyral) is sandwiched between the bent two glass plates, a pre-pressing treatment in a vacuum bag and subsequent heating and pressurizing treatments in an autoclave are carried out to produce a laminated glass in which the glass plates and the interlayer are laminated.
When a curved glass thus produced is assembled into an automobile, high shape reproducibility is required. In a case of door glass which is slidable up and down by an operation of a driver/passenger to close or open the window, a predetermined reproducibility of design shape is required. If reproducibility of the shape is poor, the glass may be collided or frictioned with e.g. metallic members to be damaged when it is slid. Further, in a case of fixed window such as a windshield or a rear window, if the reproducibility of the shape is poor, it becomes difficult to attach the glass to an opening. As a result, see-through distortion (a phenomenon that an image through a glass is distorted) or a reflection distortion (a phenomenon that an image reflected by a glass surface is distorted) may occur as a problem unique to window glasses.
To cope with these problems, heretofore, a glass plate after bending has been placed on an actual measurement inspection stand (refer to e.g. Patent Document 1) called as a gauge to carry out shape inspection, and only glass plates having a predetermined shape accuracy have been employed for production of automobiles. Such a gauge is an inspection mold having a shape formed so as to fit to a predetermined design shape of a glass attached for use, and a plurality of distance sensors are embedded in an inspection plane of the gauge. By measuring the distance from the surface of the mold to a rear surface of a glass plate, displacement of the shape of the glass plate from its design shape, is measured to evaluate the accuracy of the shape. Heretofore, an inspection using such a gauge has been carried out with respect to all or sampled formed glass plates.
However, in an inspection using a gauge, a step of placing a glass plate is required for every single glass plate, whereby improvement of productivity is limited. Further, since it is necessary to prepare a gauge for every model of final product, a large number of gauges are required to cope with production of recent various types of automobiles. Further, since such a gauge has a size equal or larger than a window glass, there is such a problem that a wide space is required to store a large number of gauges prepared for every model. There is also a problem that these gauges need to be stored for a long time considering repairment purpose in the future.
To cope with these problems, the present inventors have provided a shape inspection method solving the above problems in Patent Document 2.
This inspection method comprises a first step of calculating shape data of a glass plate in a weightless state based on actual measurement data of the glass plate in a state that the glass plate is placed on a universal inspection stand having three universal supporting points (refer to FIG. 3: universal inspection stand 110), a second step of calculating virtual shape data of the glass plate in a state that the glass plate is virtually placed on an actual measurement inspection stand (refer to FIG. 6: predetermined inspection stand 130), based on the shape data of the glass plate in a weightless state, a third step of placing the glass plate on the actual measurement inspection stand, a fourth step of obtaining information of actual measurement inspection data of the glass plate placed on the actual measurement inspection stand, and a fifth step of judging the quality of the glass plate based on the virtual shape data of the glass plate in a stat that the glass plate is placed on the actual measurement inspection stand and the information of the actual measurement shape data of the glass plate on the actual measurement inspection stand.
In the invention of Patent Document 2, by simulating the shape of a glass plate in a weightless state from the shape of the glass plate actually measured, it is possible to judge the shape quality of the glass plate without having influence of deflection caused by gravity. Further, by simulating a state in which the glass plate is placed on a predetermined inspection stand from the shape of the glass plate in the weightless state, it is possible to simulate inspections of the glass plate using these actual measurement inspection stands without actually preparing these actual measurement inspection stands. Further, since the universal inspection stand provided with the first, the second and the third supporting portions for supporting a glass plate, is an inspection stand of three point supporting type, which can always support the glass plate regardless of the shape of the glass plate, the inspection stand can be universally used.